linux-kernel - Re: [PATCH v13 0/7] cgroup-aware OOM killer

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Date:   Wed, 1 Aug 2018 09:37:23 -0700
From:   Roman Gushchin <guro@...com>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
CC:     Andrew Morton <akpm@...ux-foundation.org>,
        David Rientjes <rientjes@...gle.com>,
        Michal Hocko <mhocko@...nel.org>, <linux-mm@...r.kernel.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Tejun Heo <tj@...nel.org>, <kernel-team@...com>,
        <cgroups@...r.kernel.org>, <linux-doc@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>
Subject: Re: [PATCH v13 0/7] cgroup-aware OOM killer

On Tue, Jul 31, 2018 at 11:14:01PM +0900, Tetsuo Handa wrote:
> On 2018/07/17 9:55, Tetsuo Handa wrote:
> >> I don't get, why it's necessary to drop the cgroup oom killer to merge your fix?
> >> I'm happy to help with rebasing and everything else.
> > 
> > Yes, I wish you rebase your series on top of OOM lockup (CVE-2016-10723) mitigation
> > patch ( https://marc.info/?l=linux-mm&m=153112243424285&w=4 ). It is a trivial change
> > and easy to cleanly backport (if applied before your series).
> > 
> > Also, I expect you to check whether my cleanup patch which removes "abort" path
> > ( [PATCH 1/2] at https://marc.info/?l=linux-mm&m=153119509215026&w=4 ) helps
> > simplifying your series. I don't know detailed behavior of your series, but I
> > assume that your series do not kill threads which current thread should not wait
> > for MMF_OOM_SKIP.
> 
> syzbot is hitting WARN(1) due to mem_cgroup_out_of_memory() == false.
> https://urldefense.proofpoint.com/v2/url?u=https-3A__syzkaller.appspot.com_bug-3Fid-3Dea8c7912757d253537375e981b61749b2da69258&d=DwICJg&c=5VD0RTtNlTh3ycd41b3MUw&r=i6WobKxbeG3slzHSIOxTVtYIJw7qjCE6S0spDTKL-J4&m=h9FJRAWtCmDLT-cVwvXKCYIUVRSrD--0XFJE-OnNY64&s=If6eFu6MlYjnfLXeg5_S-3tuhCZhSMv8_qfSrMfwOQ0&e=
> 
> I can't tell what change is triggering this race. Maybe removal of oom_lock from
> the oom reaper made more likely to hit. But anyway I suspect that
> 
> static bool oom_kill_memcg_victim(struct oom_control *oc)
> {
>         if (oc->chosen_memcg == NULL || oc->chosen_memcg == INFLIGHT_VICTIM)
>                 return oc->chosen_memcg; // <= This line is still broken
> 
> because
> 
>                 /* We have one or more terminating processes at this point. */
>                 oc->chosen_task = INFLIGHT_VICTIM;
> 
> is not called.
> 
> Also, that patch is causing confusion by reviving schedule_timeout_killable(1)
> with oom_lock held.
> 
> Can we temporarily drop cgroup-aware OOM killer from linux-next.git and
> apply my cleanup patch? Since the merge window is approaching, I really want to
> see how next -rc1 would look like...

Hi Tetsuo!

Has this cleanup patch been acked by somebody?
Which problem does it solve?
Dropping patches for making a cleanup (if it's a cleanup) sounds a bit strange.

Anyway, there is a good chance that current cgroup-aware OOM killer
implementation will be replaced by a lightweight version (memory.oom.group).
Please, take a look at it, probably your cleanup will not conflict with it
at all.

Thanks!